バルク金属ガラスの長手方向超音波アシスト旋削システムの構築とその切削シミュレーション研究

Building of Longitudinal Ultrasonic Assisted Turning System and Its Cutting Simulation Study on Bulk Metallic Glass.

• Shuo Shan
• Pingfa Feng
• Huiting Zha
• Feng Feng

抄録

バルク金属ガラス(BMG)は、合金を急速に凝縮させた新しい材料です。高強度、高硬度、耐食性などの優れた特性を持つことから、金型製造や兵器などの分野での応用が進んでいます。しかし、BMGは難削材の一つであり、従来の切削加工では高精度かつ効率的に加工することが困難な材料でもあります。超音波加工は、従来の切削加工に比べて、切削力の低減、工具寿命の延長など、多くの技術的優位性を有している。超音波加工では，超音波電気信号が工具上で高周波の機械的振動に変換され，加工過程で工具と被加工物の関係が変化する．本研究では，BMG加工のために縦方向超音波アシストターニング（LUAT）システムを構築した．その共振周波数と振動特性をモーダル解析と高調波応答解析によりシミュレーションし，変位試験を行うことで，BMG加工に適した周波数と振幅の選択と検証を行った．これに基づいて，二次元旋削有限要素モデルを構築し，異なる切削速度下での超音波振動の切削力への影響を研究した．その結果，BMG加工では，加工速度が臨界加工速度以下の場合には，長手方向の超音波振動が平均切削力を大幅に減少させ，フォン・ミゼス応力も減少させることがわかった．また，切削加工中に工具先端が不連続に被加工物に接触するため，従来の旋削加工（CT）に比べて瞬間的な切削力が周期的になる．

Bulk metallic glass (BMG) is a new kind of material which is made by rapid condensation of alloy. With excellent properties like high strength, high hardness, corrosion resistance, BMG is increasingly applied in mold manufacturing, weapon equipment and other fields. However, BMG is also one of hard-to-machine materials, which is arduous to be processed precisely and efficiently by the means of conventional cutting. Compared with conventional cutting, ultrasonic machining has a multitude of technological advantages such as reducing the cutting force, extending the tool life, etc. In ultrasonic machining, the ultrasonic electric signal is transformed into high frequency mechanical vibration on the tool, which changes the relationship between the tool and the workpiece in the process of machining. In this study, the longitudinal ultrasonic assisted turning (LUAT) system is established for processing BMG. Its resonant frequency and vibration characteristics are first simulated by modal analysis and harmonic response analysis, and then tested by displacement testing experiments, so that the suitable frequency and the amplitude for BMG turning can be selected and verified. On this basis, the two-dimensional turning finite element model is established to study the effect of ultrasonic vibration on cutting force under different cutting speeds. The research manifest that during the BMG turning, the assistance of longitudinal ultrasonic vibration can significantly reduce the average cutting force as well as the von Mises stress when the turning speed is below the critical turning speed. In addition, the tip of the tool contacts the workpiece discontinuously during cutting process which makes the instantaneous turning force in LUAT more periodic than that in conventional turning (CT).